Transvenous cardiac pacemakers and ICDs using leads threaded into the right sided chambers of the heart through the venous system have evolved over the years from single chamber (one implanted lead) to dual chamber (two implanted leads); then to single and eventually dual chamber ICDs. More recently with the wider recognition of the increased incidence of heart failure secondary to right sided pacing of the heart, as well to numerous other etiologies CRT devices have been developed with left sided chamber leads delivered transvenously to endocardial locations, and/or on through the coronary sinus to left ventricular epicardial locations, and/or with a variety of transthoracic approaches to direct epicardial or intramyocardial left ventricular or left atrial stimulation sites.
In a typical prior art dual chamber defibrillator system, there is a trifurcated ventricular lead connector, with one arm providing low voltage IS-1 pace-sense function and two arms providing high voltage DF-1 connections. An advantage of this configuration was that if one of the high voltage or low voltage components of this type of lead failed, it could be corrected relatively simply by implanting a replacement single function lead, disconnecting the failed component from the pulse generator header and plugging the replacement lead's connector into that connector cavity thereby abandoning the failed lead. However, along with the AIMD, the trifurcated connector considerably increased the mass in a patient's pectoral (or other) pocket, provided the opportunity for cross connections at the time of initial implant, plus was prone to failure and increased the difficulty and risks associated with subsequent pulse generator or lead replacement/repair surgery.
The ISO 27186 Standard for DF4 and IS4 quadripolar connector systems evolved in order to replace the mechanically and functionally complex trifurcated connector with a single lead connector encompassing multiple sequential electrodes and functions, and requiring only a single set screw for lead fixation and electrical activation of the pin electrode. This minimized the number of connector cavities in, and size of, defibrillator headers simplified surgical implant procedures and reduced the risk of technical errors. However, lead conductor failures, particularly of IS4 and DF4 style leads have occurred.
Furthermore, it is not always practical to extract an IS4 or DF4 lead even if a single conductor or function has failed. The lead extraction procedure becomes particularly more difficult as the duration of implantation lengthens. Over time, the lead typically becomes adhered to tissue due to the formation of scar tissue, tissue ingrowth and the like thus requiring a more invasive procedure to be performed. Also, simply abandoning a defective IS4 or DF4 lead is problematic, because abandoning the old lead and implanting a new one can lead to venous occlusion and interference with closure of the tricuspid valve leaflets etc. Further, stacked ICD leads with large surface area high voltage coil electrodes tend to induce significant fibrous tissue reaction, binding the leads together and to surrounding tissues, and making extraction procedures even more hazardous. Yet extraction may in some cases become unavoidable because of the development of endocarditis or other complications.
Accordingly, there is a need for a novel secondary header or adaptor that facilitates restored functionality of a partially or completely dysfunctional lead and offers the added benefit of a low profile. These secondary headers or adaptors are indicated when one or more components of an implanted medical lead, particularly a DF4 or IS4 lead, has failed or become partially dysfunctional.
Failure of a medical lead conductor(s) can occur for a variety of reasons, including dislodgement at or migration from the electrode-tissue interface, complete or partial fracture or breakage of a lead conductor, abrasion or cracking or other forms of lead insulation disruption leading to low insulation resistance and low impedance measurements. Low insulation resistance can occur between a lead conductor and body fluid or between a lead conductor and adjacent lead conductors. Other reasons for failure include an increase in lead conductor impedance, an increase of the pacing capture threshold, or just the failure to deliver appropriate, effective or optimal therapy. As defined herein, a lead conductor failure may include one or more of any of the aforementioned conditions.
Adaptors of the prior art are generally of a relatively simple lead based design. They extend out into tissues away from the pulse generator pocket so that the distally inserted lead connectors are often well away from the pulse generator pocket at the time of subsequent reoperation; and even though inoperative attempts are made to wrap the added length of the adaptor and now surplus proximal lead body segments around the pulse generator and position the tangle of insulated wires behind it, postoperatively sections of insulative conductor are often prominent just beneath the skin. Patients often complain of what they feel is a doubling of implant bulk. In general, implanters fervently dislike lead based adaptors because of the mish mash of crossing conductors from the attached leads and the adaptor itself can be a nightmare to dissect out at reoperation, maximizing the probability of intraprocedural damage during reoperation. The additional electrical connections focus stresses and conductor and insulation failure are common. Stimulation of adjacent chest wall musculature is also common because of multiple poorly insulated set screw connections.
Incorporation of the low and high voltage contacts of an older trifurcated connector defibrillator lead into the newer single DF4 (or its low voltage IS4 counterpart) has a number of functional limitations, but physically DF4 is a great improvement as it: (1) reduces the total volume of the implantable system; (2) reduces the number of set screws required to connect the lead to the defibrillator; (3) reduces the need for tissue dissection within the pocket during replacement; (4) reduces lead-on-lead interactions within the implant site or pocket; and (5) eliminates the potential for DF-1 connectors from being reversed in the defibrillator header. However all of these mechanical and procedural advantages are essentially lost if there is a failure of one of the multiple lead conductors, insulation (and/or their associated electrodes) either through damage or failure to deliver effective therapy.
A failure of one lead conductor in a DF4 system leaves the physician with several bad choices. The physician can put the patient, themselves and their surgical team through a potentially difficult lead explant/extraction surgery and then put in a new DF4 lead. This is not without significant risk. Or, the implanting physician could throw away the still functional defibrillator pulse generator and try to obtain a custom replacement pulse generator with all the original connector cavities including DF4, plus an additional DF-1 connector cavity for a case where a high voltage shocking coil component of the multifunctional lead system has failed, or, plus an additional IS-1 connector cavity where a component of the low voltage pace sense multifunctional lead system has failed. If this type of device was obtainable the physician could then plug the partially defective DF4 lead connector into the new DF4 header connector cavity, implant a new DF-1 lead or IS-1 lead, as indicated and in parallel with the pre-existing DF4 lead system, and insert it into the new header's additional DF-1 or IS-1 connector cavity. However, the new ICD would cost over $20,000 and would need to be specific to not only the DF4 component failure at hand, but also to the specific subtype of ICD being replaced, i.e., single chamber, dual chamber or resynchronization. Further, to date no manufacturer has agreed to produce the series of at least 6 custom ICDs necessary to repair all combinations of lead malfunction and ICD subtypes. The cost of maintaining the whole range of replacement devices in inventory would also be high.
And even if all these issues were overcome another problem would remain. That is, the defective lead is still in place and connected to the pulse generator circuits. The sine qua non of ICD lead failure, in addition to failure of therapeutic pace-sense or defibrillation functions, which the new ICD pulse generator and lead can correct, is inappropriate and on occasion involves lethal low impedance and high intensity shocks in the 100s of volts range. By inappropriate it is indicated that the patient is shocked, often repeatedly, not because a life threatening arrhythmia has occurred but because the defibrillator sensing circuits are receiving high rate signals generated from sites of insulation failure and or from conductor fractures in the original ICD leads low voltage/pace sense components. Alternatively, if the failure had occurred in the high voltage components of the DF4 lead, the potential for short-circuiting of required life saving shocks would persist. Prior art abandoned lead components can also be problematic during MRI scans because they can pick up high-power RF induced energy which can lead to overheating of the lead and/or its distal electrode, which can heat up or even burn surrounding heart tissue.
Reference is made to U.S. Pat. Nos. 7,225,034 and 7,242,987, the contents of which are incorporated herein by reference. These patents describe a lead-based adaptor for use with DF4 pulse generators at the time of ICD and lead system initial implantation, when defibrillation thresholds indicate an inadequate safety margin. These adaptors are similar in design to prior art products in that a connector, in this case DF4, is disposed at one end and connects into an elongated insulated, lead body like segment containing 4 lead wires. This eventually bifurcates into two arms, one terminating in a DF-1 connector cavity and the other terminating in a DF4 connector cavity. This allows reuse of the DF4 lead and parallel hard wired cross connection of one or more of the high voltage outputs to one or more additional DF-1 leads to see if an improved shock vector can be obtained. The adaptors described in these patents introduce all of the previously described disadvantages and concerns related to adaptors in general but in addition will further greatly increase the bulk of a pectoral or other pocket. The '034 and '987 patents are not directed to a situation where a previously implanted lead conductor has failed. These patents are directed towards supplying additional connector cavities if additional defibrillation vectors are required and are not relevant to the post implant repair of a high voltage shocking coil or failed pace sense functions There is no provision within the '034 patent, for example, to disconnect defective lead component or components, and prevent them from interfering with sensitive AIMD circuitry and functions. FIG. 3 of the '987 patent does show a switch 110 which provides a means for reversibly decoupling the proximal high voltage electrode of the first DF4 lead from the high voltage electrode of the supplemental DF-1 lead, but this is neither permanent nor reliable, and introduction of a somewhat rigid switch component into the grip zone or lead like body of the adaptor would add complexity and focus flexural stresses with increased probability of fracture of adjacent conductors. The FIG. 3 drawing description of the '987 patent states that, “When defibrillation thresholds achieved using coil electrodes on a first lead, for example electrodes 54 and 52 of said lead 40 shown in FIG. 1, are unacceptably high such that placement of a second high-voltage lead, for example, lead 60, is required, it may be desirable to provide a high-voltage signal to the second lead without providing the same high-voltage signal to a coil electrode on the first lead. As such, switch 110 is provided between connector ring 28 and conductor 78A or anywhere along conductor 78A, which is coupled to contact 86 as shown previously in FIG. 2.” In other words, the switch of the '987 patent is directed towards optimizing therapeutic defibrillation vectors. As used in the '987 patent, the word signal refers to a high-voltage biphasic or monophasic defibrillation shock. Nowhere in the '034 or '987 patents is the problem of a previously implanted damaged or defective lead conductor or other component addressed, nor is provision made to provide a header adaptor to be able to cope with this. And, as with all prior art adaptors, such as from Oscor, or Medtronic such as described in the '034 and '987 patents, are lead based. This means that the bifurcated connector cavity terminals for receiving the bulky DF4 connector and the added DF-1 lead connector are located several centimeters along a lead away from the pulse generator. Accordingly, the pectoral or alternative site, pocket bulk is increased and all the other lead based adaptor disadvantages are preserved. In addition, the '987 and '034 patents lead-based adaptors have all of the same problems as previously described for prior art leads with trifurcated lead connectors wherein, subsequent surgery and removal of the device can be problematic. One may also go to the website of Oscor Incorporated to see an entire family of lead-based adaptors.
As previously stated, lead conductors can fail for a variety of reasons. Conductor failures and recalls of implanted leads have been common in the implantable medical device industry. An interesting exercise is to do a simple Google search using the following key words: “pacemaker lead recalls.” Literally, hundreds of “hits” come up. It has been common in the implantable medical device industry to abandon a defective lead and simply implant a new one roughly in parallel with it through the venous system.
There are a number of problems with abandoned leads, including the problem of MRI RF field-induced overheating of such a lead or its distal electrode. Implanted leads are generally less dangerous when they are connected to a pulse generator (as in the'987 and '034 patents except for the switch being open). The reason for this is that prior art pulse generators, including pacemakers and defibrillators generally have a feedthrough filter capacitor at the point of lead conductor ingress through the hermetic seal of the active implantable medical device. At high frequencies, such as for MRI RF pulsed frequencies, this EMI filter provides a low impedance path between the lead conductors and the AIMD housing which acts as an energy dissipating surface. Accordingly, in a high power MRI environment, much of the RF energy that is induced in the lead is diverted by the feedthrough capacitor where it is dissipated as a small temperature rise on the relatively large surface area of the pacemaker housing, which is usually a titanium can. However, when a lead is abandoned, there is no place for this MRI RF energy to go other than at the distal tip electrode, which can still be in contact with biological cells. This can lead to significant overheating. For additional information regarding the danger of abandoned lead conductors, one is referred to a published paper entitled, PACEMAKER LEAD TIP HEATING IN ABANDONED AND PACEMAKER-ATTACHED LEADS AT 1.5 TESLA MRI, published in the Journal of Magnetic Resonance Imaging 33:426-431 (2011).
Accordingly, what is needed is a low profile secondary header or adaptor that maintains close and compact apposition to the implantable medical device or pulse generator housing and/or its header and at the same time, disconnects the malfunctioning lead components from the pulse generator circuitry. The abandoned lead conductor(s) and its components should be connected to an MRI energy dissipating surface of the secondary header, and the secondary header should closely conform to the implantable medical device so as to minimize the in-growth of any intervening fibrous scar or mesothelial tissue.
There is also a need for a low profile secondary header or adaptor that conforms to the immediately adjacent and apposed therapy delivery apparatus, provide a receptor connector cavity allowing for insertion of the partially failed DF4 or IS4 (or equivalent) lead connector and thereby continued use of the selected, still functional components of a multifunctional implantable medical device lead, injector catheter or other chronically implantable, partially multifunctioning therapy delivery device. Such a compact, secondary header is needed which may provide one or more additional connector cavities wired for the functions disconnected from the DF4 or IS4 lead for insertion of the connectors of a new or reused lead or leads. Further, such a device is needed which allows continued use of an implanted lead, such as a DF4 or IS4 lead, which has partially failed, so as to eliminate the necessity for entirely replacing the failed lead, while simultaneously allowing the implantation of a supplemental lead to correct for the original leads failure.
The present invention fulfills these needs and provides other related advantages.